Membranes membrane fusion

Why should contact between shrunken cells be damaging One possibility is that the contacts induce damaging membrane-membrane fusion, for close contact between shnmken cells has been found to induce membrane fusion above 0 °C. Moreover, freezing has been shown to induce fusion in model membranes (Anchor-doguy et al., 1987) and to produce changes in fungal hyphae that are symptomatic of fusion (Fujikawa and Miura, 1986). 

The depolarization that accompanies the action potential induces an increase in membrane permeability to calcium ions. A large inward electrochemical gradient exists for calcium and it moves into the terminal. The calcium that enters the terminal activates enzymes that cause the attachment of some of the vesicles to releasing sites on the terminal membrane, membrane fusion, and the release of the vesicular contents into the synaptic cleft. Transmitter release is terminated by the removal of calcium from the terminal cytoplasm, either via a calcium pump, which pumps it out of the cell, or by uptake into the endoplasmic reticulum or into mitochondria. 

We have previously shown that binding of the liposomes to red cells can considerably be enhanced (20-25-fold) by covalently attaching F(ab )2 fragments of a mouse polyclonal antibody, raised against the erythrocytes membrane, to their surface (20,21). We further demonstrated that at least 20-30% of the cell-bound liposomes delivered their contents to the target cells, presumably by membrane-membrane fusion (21) and this amounts to only 2.5% of the initially injected dose of liposomes. 

The phenomenon of membrane fusion may be considered as demonstrating four phases. Although mutually interdependent, they are considered separately for ease of presentation (a) approximation of bila-mellar membrane organelles (b) phase of membrane contact (c) membrane-membrane fusion and content translocation and (d) intrinsic membrane factors allowing for specificity in membrane fusion. 

Knoll G and Plattner H 1989 Ultrastructural analysis of biological membrane fusion and a tentative correlation with biochemical and biophysical aspects Electron Microscopy of Subcellular Dynamics ed H Plattner (London CRC) pp 95-117... 

The adliesion and fiision mechanisms between bilayers have also been studied with the SEA [M, 100]. Kuhl et al [17] found that solutions of short-chained polymers (PEG) could produce a short-range depletion attraction between lipid bilayers, which clearly depends on the polymer concentration (fignre Bl.20.1 It. This depletion attraction was found to mduce a membrane fusion widiin 10 minutes that was observed, in real-time, using PECO fringes. There has been considerable progress in the preparation of fluid membranes to mimic natural conditions in the SEA [ ], which promises even more exciting discoveries in biologically relevant areas. 

Bullough, P.A., et al. Structure of influenza haemagglu-tinin at the pH of membrane fusion. Nature 371 37-43, 1994. 

Currently, five different molecular classes of mdr efflux pumps are known [5], While pumps of the the ATP-binding cassette (ABC) transporter superfamily are driven by ATP hydrolysis, the other four superfamilies called resistance-nodulation-division (RND), major facilitator superfamily (MFS), multidrug and toxic compound extrusion (MATE), and small multidrag resistance transporter (SMR) are driven by the proton-motive force across the cytoplasmic membrane. Usually a single pump protein is located within the cytoplasmic membrane. However, the RND-type pumps which are restricted to Gram-negative bacteria consist of two additional components, a periplasmic membrane fusion protein (MFP) which connects the efflux pump to an outer... 

While the basic features of SNARE assembly and disassembly provide a convenient framework for explaining how membrane fusion works, both the regulation of SNAREs and the molecular details of fusion are not well understood. Most is known about the neuronal SNAREs that mediate regulated membrane fusion of synaptic vesicles and of secretory granules in neuroendocrine cells. They include synaptobrevin2, localized to the synaptic vesicle, and SNAP25 ( SNAPs) and syntaxinlA, both of which are localized to the plasma... 

While recent attention has been largely on proteins, it should be borne in mind that membrane fusion ultimately involves the merger of phospholipid bilayers. However, little is known about the specific membrane lipid requirements. When membranes fuse, energetically unfavorable transition states are generated that may require specific lipids and lipid domains for stabilization. Although there is some evidence for a specific influence of lipids on exocytosis, it is still unclear whether specific lipid metabolites are needed or even generated at the site of membrane merger. 

Jahn R, Siidhof TC (1999) Membrane fusion and exocytosis. Annu Rev Biochem 68 863-911... 

Chen YA, Scheller RH (2001) SNARE-mediated membrane fusion. Nat Rev Mol Cell Biol 2 98-106... 

Koumanov F, Jin B, Yang J et al (2005) Insulin signaling meets vesicle traffic of GLUT4 at a plasma-membrane-activated fusion step. Cell Metab 2 179-189... 

Sollner TH (2004) Intracellular and viral membrane fusion a uniting mechanism. Curr Opin Cell Biol 16 (4) 429-35... 

Previous studies indicate that osmotic gradients promote membrane fusion, while hyperosmotic conditions inhibit membrane fusion during exocytosis. Consistent with this idea is the observation that the release of lysosomal enzymes from rabbit neutrophils, induced by the chemotactic peptide J -formylmethionyl-leucyl-phenylalanine (FMLP), is inhibited almost 80% in a 700-mosmol/kg medium. Inhibition is immediate (within 10 s), increases with osmolality, and is independent of the osmoticant. Neutrophils loaded with the calcium indicator indo-1 exhibit an FMLP-induced calcium signal that is inhibited by hyperosmolality. Hyperosmolality (700 mosmol/kg) increases basal calcium levels and reduces the peak of the calcium signal elicited by FMLP at concentrations ranging from 10 ° to 10 M. 

KieUan M, Rey FA (2006) Virus membrane-fusion proteins more than one way to make a hairpin. Nat Rev Microbiol 4 67-76... 

Skehel JJ, Wiley DC (2000) Receptor binding and membrane fusion in virus entry the influenza hemagglutinin. Ann Rev Biochem 69 531-569... 

Liposomes have been widely used as model membranes and their physicochemical properties have therefore been studied extensively. More recently, they have become important tools for the study of membrane-mediated processes (e.g., membrane fusion), catalysis of reactions occurring at interfaces, and energy conversion. Besides, liposomes are currently under investigation as carrier systems for drugs and as antigen-presenting systems to be used as vaccines. 

Downstream of early FceRI-induced signaling events (such as Ca + influx), the final stages of mast cell degranulation require membrane fusion events. The exocytosis of... 

Q Studies using v- and t-SNARE ptoteins reconsti-mted into separate lipid bilayer vesicles have indicated that they form SNAREpins, ie, SNARE complexes that hnk two membranes (vesicles). SNAPs and NSF are required for formation of SNAREpins, but once they have formed they can apparently lead to spontaneous fusion of membranes at physiologic temperamre, suggesting that they are the minimal machinery required for membrane fusion. 

Influenza virus hemagglutinin Responsible for host-cell attachment and membrane fusion... 

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